Drilling fluid for heaving shale



UNITED STATES PATENT OFFICE 2,474,329 DRILLING FLUID FOR HEAVING SHALERichard A. Salathiel, Houston, Tex., assignor, by mesne assignments, toStandard Oil Development Company, Elizabeth, N. J a corporation ofDelaware No Drawing. Application January 13, 1948, Serial No. 2,139

4 Claims. (Cl. 2528.5)

This invention relates to a drilling fluid which disintegratescontinuously to such an extent as to will effect a minimum ofdisintegration of heavin rf re w h r llin p on ing shale. The rates ofdisintegration of sloughing and In the rotary drilling of oil and gaswells fluid heaving shales may be decreased when using conis pumped downthe drill stem to the drill at the Ventional drilling muds by addingmaterials which Working face in the bottom of the bore. Th reduce therate of filtration loss and improve annular space between the drill stemand the ties from shale disintegration are encountered borehole walls.In some areas, as for example 1.0 occasionally and serious holeenlargement in shale cessfully by the ordinary rotary drilling methodsdrilling fluids, the methods heretofore practiced when using common mudfluids. These shales have not been entirely satisfacto Not the leasthave a tendency to disintegrate by swelling or of the disadvantages ofsuch methods is the high cracking or both so that the walls of the holeare cost of materials required in their practice.

unstable and material sloughs into the hole or It is an object of thisinvention to P d t moves into the hole by swelling. The caving ordrilling fluid for the drilling of boreholes into cracking caused by thepresence of seams or thin the disintegration thereof.

layers of readily hydratable and swellable ma- In accordance with thepresent invention the terial closely interbedded with harder and lessdisintegration of heaving shale is prevented by readily hydratable shalematerials. In many employing a drilling fluid consisting of water, Casesn the pa t filling 0 h bo eho e, 0 parts clay, alkali metal hydroxide,salt, and materials of it, have resulted in stuck drill pipe and abanforpromoting the efiectiveness of the hydroxide donment of further eifortsto make additional in preventing disintegration of shale. Instead ofhole. It is common in drilling shale sections addin the alkali metalhydroxide, salt and a mawh ch d no w ll or slou h v re y enough toterial for promoting the effectiveness of the hystop drilling operationsor even to cause extreme droxide t a mixture of water and clay, th

difliculty to observe extensive enlargements of the materials may beadded to ordinary drilling mud borehole or even the formation ofsubterranean provided the drilling mud contains a suitable cavities. Inthese cases although the materials amount of clay to give a fluid havingthe desired which swell, slough or cave into the hole are reyield pointand Viscosity after the above moved by the arming fluid the enlargedholes and tioned constituents have been added. Finely dicavities whichare formed interfere to various devided material Such as barytes, ironoxide, and grees with operations involved in drilling and the like maybe used to supplement the c1 ay in completing the well. When suchenlargements formingthe drilling mud and (.mvmes are formed the rateof.flow of h Anumber of different materials may be used for mud sgreatly reduced and the carrying ca promoting the effectiveness of thealkali metal thereof is diminished. To increase the rate of hydroxideemployed and I have found that the pumps having a large excess capacitymust alkali metal salts of weak inorganic acids are 2: 0 5 2 5 3 51223232 2 3 22 65 2 8? 2 particularly suitable. Of these sodium carbonatement are required in order to obtain a proper 15 9 y an efiectlvePromoter but 15 also sealing 2"? l With? $23??? 1333; fj i oiumsupieanlSOlmpO a a tcg23553 3; a i g a i s lie li y grgtigif 3f been found togive t d esults for promoting the h l adjacent th borehole by watercontained effectiveness of alkali metal hydroxide in the drillin theordinary drilling mud. Thus, a heaving ing of v n shale f rma ions. 0fg,ou1 s the shale may be defined as oneiwhich in ontact potassium OIlithium salts Of weak 11'101' amc aCldS with the usual water basedrilling fluids swells or may be employed although they are somewhatmore expensive than the corresponding sodium salt.

It is known that when shales are immersed in suitably strong solutionsof alkali metal hydroxides they do not swell. Tests made by placingsamples of shales in solutions of sodium hydroxide showed that whensubstantially less than the optimum concentration of sodium hydroxidewas used, swelling and sloughing still occurred and little advantage wasgained. It was also observed that when substantially more than theoptimum concentration of sodium hydroxide was used swelling did notoccur but cracking was observed which weakened some of the shales. Shalesamples differed among themselves in the optimum concentration of sodiumhydroxide solutions required for their preservation. These optimumconcentrations for the different shale samples tested varied within thelimits of and 30% by weight of sodium hydroxide. It was further observedthat the amount of sodium hydroxide required to preserve a particularshale could be decreased by adding sodium chloride, a much lessexpensive material, to the solution. With concentrations of sodiumhydroxide and sodium chloride above the optimum, as with the sodiumhydroxide solutions, cracking of some of the shales occurred. It wasstill further observed that the addition of small amounts of certainsalts to the caustic alkali solutions or to the solutions of sodiumchloride and caustic alkali, of more than sufficient concentration toprevent swelling, served to prevent cracking of the shales and thusadapted the solutions to preserving a wider range of shale types. Forexample, I have found that a fluid consisting of 70.3 weight percentwater, 8.25 weight percent sodium hydroxide, 4.15 Weight percent sodiumcarbonate, and 17.3 weight percent sodium chloride is substantiallyequivalent to a weight percent solution of sodium hydroxide from thestandpoint of preventing the swelling of clay and shale samples andsuperior to such a solution from the standpoint of cracking of some ofthe shale samples. Thus, the use of a material such as sodium carbonategreatly reduces the cracking of shales contacted by alkali hydroxidesolutions. It has further been found that the use of sodium carbonatemakes any given caustic-brine solution effective over a wider range ofshale types than is the case when no such promoter material is used.

It is to be understood that the amount of material for promoting theeffectiveness of the hydroxide to be employed in the drilling fluid mayvary within a substantial range depending largely on the character ofthe shale encountered. The minimum concentration of the electrolyteswhich will be effective in any particular case may be determined byexperimentation, that is, by obtaining a sample of the shale throughwhich drilling is to be accomplished and observing its rate or degree ofdisintegration by the action of water-containing various concentrationsof the materials. When optimum amounts are incorporated in the drillingmud, the rate of disintegration of the shale sample will be negligible.In general, the amount of alkali metal hydroxide may be varied fromabout 6% to about 15% by weight of the total fluid, and when suchconcentrations are utilized, the amount of the material for promotingthe eifectiveness of the alkali metal hydroxide may vary from about 1%to about 10% based on the total fluid, the preferable range of thelatter being from about 2% to about 6%.

The concentration of the alkali metal hydroxide required will generallyincrease as the drier shales are encountered in deep, high temperatureformations. Salt is added to the fluid in quantities sufficient tosubstantially saturate the fluid after the alkali meta1 hydroxide andthe promoter material have been dissolved therein.

Although any alkali metal hydroxide may be employed, it is preferable touse sodium hydroxand cheapness. Although any of the previously mentionedmaterials for promoting the effectiveness of the hydroxide may beemployed, I prefer to use sodium carbonate not only because it isslightly superior but also because of its ready availability. Eithercommercia1 salt or pure sodium chloride may A solution representative ofthose effective in preserving a wide variety of shales contains 70.3weight percent water, 8.25 weight percent sodium hydroxide, 4.15 weightpercent sodium carbonate and 17.3 weight percent sodium chloride. Thissolution at about 75 F. has a specific gravity of 1.25 and a viscosityof about 4.7 centipoises. While clays do not disperse readily intosolutions of this kind, it is easily possible to prepare muds havingsuitable viscosity and gel properties by dispersing clay into waterbefore adding the electrolytes to provide an aqueous phase of thedesired composition. The following are examples of muds so prepared inwhich the aqueous phase contained 70.3 weight percent water, 8.25 weightpercent sodium hydroxide, 4.15 weight percent sodium carbonate and 17.3weight percent sodium chloride:

17 O. P. 25 C. P. S. Vis. S. Vis. Mud Mud Per cent of Fluid 93 Per centof El Paso Clay 4 5 Per cent Wy. Bentonite Clay 1 2 The mud referred toabove as having 17 centipoises viscosity (at 600 rpm Stormer) had anextrapolated yield value of 18 grams Stormer while the 25 centipoiseviscosity mud had an extrapolated yield value of 24 grams Stormer.filtration rate of the 25 centipoise viscosity mud was 66 cos. in 30minutes at pounds as tested on the standard API low pressure mud tester.Additions of small amounts of starch to muds of this type decrease thefiltration rate greatly. For example, addition of 1.2% of pearl starchto a mud prepared in the same way as those described above but whichcontained 4% of El Paso clay as the only clay component provided a mudfluid of the following properties: Viscosity, 41 centipoises;extrapolated yield value, 23 grams Stormer; API filtration rate, 6 cos.(30 minutes at 100 pounds).

Gelation rates of the caustic-brine-promoter muds are high making itdesirable to keep the yield values of such mud fluids as low as possiblewhile holding the desired solids in suspension. By so doing, gas or aircutting of the mud are avoided and at the same time sand and cuttingsmay easily be separated from the mud at the surface.

It will be apparent from the above data that drilling fluids havingdesirable viscosities and yield values may be prepared from clay withwater containing sodium hydroxide, brine, and sodium carbonate.Viscosity and yield value may, of

course, be controlled by controlling the amount for promoting of clay inthe drilling fluid. These Values will be influenced by the type of clayused and normally it will be desirable to use the clay produced from theborehole. In general, the clay content of the fluid will not be lessthan 2% nor exceed about although in some instances it will beunderstood that the clay content may be somewhat less or somewhatgreater than these values.

It will be further understood that in the practice of my invention othermaterials may also be added to form the drilling mud. For example, if aheavily Weighted mud is required it may be necessary to add weightinmaterials such as barytes, iron oxide and the like. In addition,treating agents such as sodium-hexametaphosphate, tannin, and the like,may also be included in the drilling fluid.

The nature and objects of the present invention having been thusdescribed, what is claimed as new and useful and is desired to besecured by Letters Patent is:

1. A drilling fluid for preventing the hydrous disintegration of shalescomprising clay, water, 6 to sodium hydroxide by weight based on thefluid, 1 to 10% by weight based on the fluid of an alkali metal salt ofa weak inorganic acid the efiectiveness of the sodium hyhydroxide is analkali metal sulphite.

4. A composition in accordance with claim 1 in acid for promoting theefiectiveness of the sodium phosphate. RICHARD A. SALATHIEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,044,758 Cross et al June 16,1936 2,073,413 Cross et a1 Mar 9, 1937 2,109,858 Cannon Mar. 1, 19382,191,312 Cannon Feb. 20, 1940

